1. Field of the Invention
The present invention relates to a surface acoustic wave device, for example, used for a resonator or a band-pass filter.
2. Description of the Related Art
In duplexers (DPXs) and RF filters used for mobile communication systems and other suitable systems, both a broad bandwidth and good temperature characteristics are required. As a surface acoustic wave device that has both a broad bandwidth and good temperature characteristics, for example, International Publication No. WO2006/011417 discloses a surface acoustic wave device including an IDT electrode made of Al embedded in a LiTaO3 substrate. By embedding an IDT electrode in a piezoelectric substance as in the surface acoustic wave device disclosed in International Publication No. WO2006/011417, a large electromechanical coupling coefficient (k2) is obtained. As a result, a broad bandwidth is achieved.
In a surface acoustic wave device in which an IDT electrode is embedded in a piezoelectric substance, in order to obtain a larger electromechanical coupling coefficient (k2), it is preferable to increase the density of the IDT electrode. Furthermore, from the standpoint of decreasing the insertion loss, it is preferable to form electrode fingers of the IDT electrode with a relatively larger thickness using a low resistance material so that the resistance of the electrode fingers is decreased.
However, when the density of the IDT electrode is increased or the thickness of the IDT electrode is increased, the acoustic velocity of the surface acoustic wave tends to decrease. Therefore, when a surface acoustic wave device using a surface acoustic wave in an RF range, for example, in the range of several hundred megahertz to several gigahertz, is manufactured, it is necessary to reduce the pitch of electrode fingers of the IDT electrode. If the pitch of electrode fingers is reduced, the resistance to static electricity of the surface acoustic wave device tends to decrease.